One of the client's concerns while discussing my graduation project is that 3D models can be quite expensive and might not be worth the additional cost. If the new animation technique proves to be useful, it would be in the client's interest to use the 3D model as effectively as possible. This resulted in the following sub-question.
How can 3D models, who are used for animating the animatronic, be used for other steps in the creation process of animatronics?
The following topics describe methods to incorporate a 3D model into various processes.
Prototyping with 3D printing
One of the great things about 3D printing is the ability it grants to try out different iterations of an idea without a lot of man-hours involved. Testing different material densities, changing the scale, or making changes in the design; It is all possible. Once the model or printing settings are adjusted, you click print and wait until it is done printing.
Depending on the use of your 3D print, you can adjust the density of the infill or chose another material. Lowering the infill percentage reduces printing time and material used but results in a weaker model at a certain point. Therefore I recommend doing this for models that aren't used for mechanical purposes.
Creating a base
In my post, Which components are commonly used to create animatronics?, different steps of the creation process of animatronics are described. One of the techniques described in this post is milling. Milling uses the data from a 3D model to determine how far to cut into the foam. The result is a relatively detailed copy of the 3D model, which can be further enhanced by applying clay.
For those who don't have access to a milling machine but have a 3D printer at home, the process can be replicated. Instead of milling the 3D model, a 3D print can be made. This print can be used as a base too for further detailing with clay.
Both applications use the 3D model's data to create a base. There are some differences, however. The benefit of having the model milled out of foam is that the foam itself can be easily adjusted by subtractive sculpting. A 3D print is adjustable to some degree but doesn't allow for much change. Meaning that subtractive sculpting isn't an option when you use a 3D print unless the object is adjusted digitally and reprinted. Another difference to keep in mind is the maximum size a model can be milled. This is larger than a regular 3D printer can print. It is possible to print an object in pieces and combine them afterward, but its size will still be limited. Therefore I recommend using the 3D printer method for relatively small objects, unlike the milling machine. Both the foam model and 3D printed version are lightweight. If the right infill percentage is used, the 3D print won't collapse under the clay's weight.
The benefit of using a 3D model for the animatronic's base, specifically a 3D printed base, is that you can adjust its sizing to fit the mechanics beforehand. Once the artist is finished sculpting, the mechanics still should fit in its shell. This method allows for both artists and mechanics to work at the same time.
Using either of the techniques will help the artist establish a silhouette faster so they can proceed to add detail.
Using 3D prints for casting and mold making
Mold making is used to duplicate an object by making a negative copy of the model. The negative mold is then used to cast a positive, recreating the original object. The benefit of this process is that it's easy to create duplicates of the item, but it is also possible to change the material properties of the original object. Use a transparent material like resin to create a see-through object, a rubber or silicone material to create a flexible object or even chocolate for an edible replica.
As seen in Which components are commonly used to create animatronics?, mold making and casting are widely used in the creation of animatronics. Eyes, teeth, and skin are often molded and cast. Using 3D models in this process should be possible.
Generally, a sculpt made out of clay is molded and cast. If the cast has a mechanical function, it is important that its measurements are correct. This is difficult when working with clay. Instead of using a clay sculpture, I propose to use a 3D print instead. The benefit of using a 3D print over a clay sculpt is that the 3D print preserves any detailed measurements that are made during modeling. Once printed, it possible to try-out its fitting before the mold and casting process. Test fitting a clay sculpt is hardly possible due to its pliable material properties.
For making a mold, the digital model or parts of it are 3D printed. The print is then cleaned up by filling print layers and sanding it smooth. These steps are repeated until satisfaction. This process must be done well since every blemish is transferred to the mold and, therefore, the cast.
Before the mold is made, it needs to be determined if the objects need to be molded in multiple sections or if one mold suffices. This determines what kind of mold needs to be created.
1 part mold
The cleaned print is placed inside a tub and positioned so that air pockets are minimized. A mold-making material like silicon, for example, is poured inside the tub and left until set. Once the material is set, the original model is released, and the mold is ready for casting.
Figure 1. Rough 3D print, cleaned print, mold, and cast [Own work]
2 part mold
For some objects, a one-part mold doesn't suffice. For these objects, the mold is split into 2 parts. Once both parts of the mold are made, they are placed back together. To ensure that the mold is aligned, most two-part molds are made with keys. These keys are small indentations and extrusions in the silicon mold that prohibits the mold from closing when it isn't aligned properly. If you would like to know more about making your own 2 part mold, I suggest watching this video.
Figure 2. A two-part mold with keys [Own work]
I call these molds "Box molds" since they are often placed inside a random container I have laying around. The downside of these containers is that they are often too large. Therefore, they need more silicon to be filled. Since silicon is quite expensive, it is a best practice to use a fitting mold container. Larger models are cast with a different technique called "brush-on" mold-making to save material.
Brush-on mold making
The technique "brush-on" is often used when an object is too big or complex for a one-part or two-part mold. A thin layer of silicon is carefully brushed on the objects. The first layer of silicon is more flowing than regular silicon so that it is able to go into small crevices to ensure a smooth and detailed surface.
Multiple layers are applied to thicken the silicone mold. This mold won't keep its shape by itself, unlike the box molds shown previously. To ensure the mold's shape, a mold jacket is made. Mold jackets can be made from a list of different materials, Like plaster or fiberglass, as long as it is strong enough to keep its shape. This jacket holds the brushed-on mold during casting.
3D Printing the outer shell or container
bar_el_studio used a new innovating way to create his complex molds which are documented on his Instagram. Instead of making the mold and then its outer shell, he 3D printed an outer mold shell that will hold the mold and then injects it with the mold material. bar_el_studios (2021) writes, "It makes the job very efficient, material saving and clean."
Figure 3. 3D printed outer shell bar_el_studio (2021)
Once the master model is placed inside the outer shell, the mold material can be injected.
For this technique, the original model can be used with some adjustments. The benefit of having a 3D printed shell is that it allows for digital planning of seams, pouring holes, vents, and closing mechanisms. It also allows for predetermining the thickness of the mold. The 3D print itself doesn't need much cleaning since it only holds the silicon mold. It can also be argued that this method of 3D printing an outer shell is faster than creating the mold and outer shell traditionally, but this depends widely on printing settings. Using the 3D printing technique allows for effortless duplication of the shell.
A downside that comes with using 3D prints is that the material doesn't allow for any heat treatment due to the material's relatively low melting point of 173Cº for PLA (Roberts, 2021).
List of references
bar-el-studios. (2021, February 7). I made a hard shell (jacket) for the hands and feet so I can pour rubber inside where then I’ll [Instagram post]. Instagram. https://www.instagram.com/p/CLAK-WpAekJ/
Roberts, S. (2021, March 2). PLA Filament: Strength, Temperature, and Benefits [2020]. BCN3D Technologies. https://www.bcn3d.com/pla-filament-stands-for-strength-temp/
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